We're going to turn, now, to a serious medical threat for one of the world's top athletes. Superstar Ian Thorpe is battling an infection that could cost him his career even his arm. Paula Faris with details. Thorpe said he got this infection in the hospital. Reporter: It's stunning how he contracted that infection. Ian Thorpe is in a hospital this morning receiving, what we're told is the best care possible. But even that might not be enough to prevent the former swimming champion from losing what he loves the most. He's one of Michael Phelps biggest rivals with five olympic gold medals and 22 world records. The hardest-working athletes in the sport. Reporter: This morning, Ian Thorpe's future as a competitive swimmer could be sinking. The swimming legend is being treated in his native Australia for a dangerous infection. Some media reports say the disease is similar to the potentially deadly mrs infection. And that it's so bad, he might risk losing use of his left arm. Always intend to get back in the pool. Reporter: James Erskin telling the press that he is quite sick. Serious but not life-threatening, after a series of shoulder surgeries. Hospitals are dangerous places. That's where the bad bugs live. 1 in 25 people that go into the hospital will pick up an infection. A lot from surgery. Reporter: Thorpe is a hero in his native Australia, where swimming is a national sport. And the press follows his every move. He is Michael Phelps. He is Michael Jordan. He's the biggest deal in Australian sports. Reporter: This is the latest setback for a man who has been treading water since 2006. He failed in a comeback in the 2012 olympics. And earlier this year, was treated for depression at a rehab facility. Ian Thorpe, this olympic god. How sad that he's fighting this. He's dealing with this infection. He's in a hospital bed. He's gone through a lot. Reporter: An irony that could knock this swimming great out of the water for good. Now, his management team tells us he remains in good spirits, considering the circumstances. And hopes to be back on his feet soon. But you heard Dr. Besser say, that's where the bad bugs live, in the hospitals. Paula, thanks very much.

This transcript has been automatically generated and may not be 100% accurate.

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